Double-layer vegetation canopy full-wave band reflectivity radiation transmission calculation method and double-layer vegetation canopy full-wave band reflectivity radiation transmission calculation system

Abstract

The invention belongs to the technical field of remote sensing, and provides a double-layer vegetation canopy full-wave band reflectivity radiation transmission calculation method, which comprises the following steps: S1, based on a bidirectional porosity theory, obtaining double-layer canopy single reflectivity; s2, based on a spectrum invariant theory, obtaining double-layer canopy multiple reflectance; s3, obtaining the total reflectivity of the double-layer canopies based on the single reflectivity of the double-layer canopies and the multiple reflectivity of the double-layer canopies. The invention also correspondingly provides a double-layer vegetation canopy full-wave band reflectivity radiation transmission calculation system. According to the method, multiple scattering of the directional double-layer vegetation canopies is calculated through the spectrum invariant theory, a complex layer scattering matrix does not need to be calculated, the principle is simple, and precision is high.

Description

Technical Field

[0001] This invention belongs to the field of remote sensing technology, specifically relating to a method and system for calculating the full-band reflectivity radiative transfer of a double-layered vegetation canopy. Background Technology

[0002] Forests and crops typically exhibit vertical optical and structural heterogeneity at different growth stages. For vegetation canopies with a distinct two-layer structure, simulating reflectivity using a single-layer canopy radiative transfer model (e.g., averaging leaf optical and canopy structural parameters from both the upper and lower canopies) will lead to significant errors. While three-dimensional radiative transfer models offer advantages in simulation accuracy, they are computationally resource-intensive and often require a large number of difficult-to-obtain input parameters. In contrast, one-dimensional radiative transfer models are simpler, more computationally efficient, and can quickly simulate the reflectivity of two-layer vegetation canopies, and are widely used for inverting the structural parameters of two-layer vegetation canopies.

[0003] Existing one-dimensional two-layer canopy radiative transfer models are mainly based on the four-flow theory to calculate multiple scattering. This theory assumes that multiple scattering is isotropic and approximates the vegetation radiative transfer equation using four differential equations, corresponding to the flux in the direct solar radiation direction, the flux in the observation direction, and the upward and downward isotropic diffuse scattering flux, respectively. 4SAIL2 and ACRM are both two-layer vegetation canopy radiative transfer models built on the four-flow theory: first, they use eigenvector decomposition to solve the system of differential equations to calculate the scattering matrices of the upper and lower canopies separately; then, they use a superposition method to calculate the total scattering matrix of the two canopies. Building upon the ACRM framework, MRTM and AddingS recursively apply the superposition method to calculate the scattering matrix of continuous composite layers, extending the two layers into a multi-layer structure. The multi-layer canopy radiative transfer model mSCOPE is also based on the four-flow theory, but it uses a new strategy based on the superposition method to avoid the complex process of solving the scattering matrices of different layers in a vertically heterogeneous canopy. Although mSCOPE simplifies the calculation process, it only considers the vertical heterogeneity of leaf optical properties and not the vertical heterogeneity of canopy structural features. In the near-infrared band, multiple scattering from dense vegetation accounts for more than 50% of the total scattering. Therefore, accurately simulating the multiple scattering process in a two-layered canopy is crucial for improving the accuracy of reflectance simulation. When the leaf area index (LAI) is high, the assumption of isotropic multiple scattering in the four-flow theory will lead to deviations in the simulation results, making it impossible for two-layered models based on the four-flow theory to accurately simulate the reflectance of a two-layered canopy. Furthermore, the principles behind such models are complex. In contrast, the spectral invariance theory, utilizing the optical properties of leaves and spectral invariants, can efficiently and accurately simulate directional multiple scattering processes, providing a simpler and more practical framework for canopy radiative transfer modeling. This theory is currently widely used in the construction of single-layered canopy radiative transfer models and provides new ideas for extending it to the construction of more complex two-layered canopy radiative transfer models. Summary of the Invention

[0004] To address the problems in the background art, the present invention provides a method for calculating the full-band reflectance radiative transmission of a double-layered vegetation canopy, comprising: S1, obtaining the single reflectance of the double-layered canopy based on the bidirectional porosity theory; S2, obtaining the multiple reflectance of the double-layered canopy based on the spectral invariance theory; and S3, obtaining the total reflectance of the double-layered canopy based on the single reflectance and the multiple reflectance of the double-layered canopy.

[0005] On the other hand, the present invention also proposes a method for calculating the full-band reflectance radiative transmission of a double-layered vegetation canopy, comprising: S1, obtaining the reflectance and transmittance spectra of the upper and lower canopy leaves based on the leaf spectral vectors of the upper and lower canopy; S2, obtaining the soil reflectance spectrum based on the soil reflectance spectral vector; S3, calculating the single reflectance of the double-layered vegetation canopy using the bidirectional porosity theory based on the reflectance and transmittance spectra of the upper and lower canopy leaves and the soil reflectance spectrum; S4, calculating the multiple reflectance of the double-layered vegetation canopy and its relationship with the soil background using the spectral invariance theory based on the reflectance and transmittance spectra of the upper and lower canopy leaves and the soil reflectance spectrum; S5, merging the single reflectance and multiple reflectance to obtain the reflectance of the double-layered vegetation canopy.

[0006] The present invention also proposes a full-band reflectivity radiative transfer calculation system for a double-layer vegetation canopy, which includes a computer-executable program that performs the method described above when the program is executed.

[0007] In one embodiment, the method of the present invention uses the General Spectral Vector-Leaf (GSV-L) and the General Spectral Vector Soil Reflectance (GSV) model to calculate the leaf and soil spectra of the upper and lower canopies, respectively. It uses the bidirectional porosity theory to calculate the single reflection of the double-layer vegetation canopy and the spectral invariance theory to calculate the multiple reflections between the double-layer vegetation canopy and the soil background. This method can accurately simulate the reflectance of double-layer vegetation canopies with different leaf spectral characteristics and canopy structure features.

[0008] In a preferred embodiment, the CANOP model couples the Universal Spectral Vector Leaf Model (GSV-L) and the Universal Spectral Vector Soil Reflectance Model (GSV), requiring fewer leaf and soil input parameters and allowing the focus to be on retrieving canopy structure parameters from remote sensing data.

[0009] The beneficial effects of this invention include: compared with the complex principle of the double-layer vegetation canopy radiative transfer model based on the four-flux theory and the assumption that multiple scattering is isotropic, this invention uses the spectral invariance theory to calculate the multiple scattering of the directional double-layer vegetation canopy, without the need to calculate the complex layer scattering matrix, and is simple in principle and highly accurate. Attached Figure Description

[0010] To facilitate understanding of the invention, it will be described in more detail with reference to the specific embodiments shown in the accompanying drawings. These drawings depict only typical embodiments of the invention and should not be considered as limiting the scope of protection of the invention.

[0011] Figure 1 This is a flowchart illustrating one embodiment of the method of the present invention.

[0012] Figure 2 This is a flowchart illustrating another embodiment of the method of the present invention.

[0013] Figure 3 This is a flowchart illustrating another embodiment of the method of the present invention. Detailed Implementation

[0014] The embodiments of the present invention are described below with reference to the accompanying drawings to enable those skilled in the art to better understand and implement the present invention. However, the listed embodiments are not intended to limit the present invention. In the absence of conflict, the following embodiments and the technical features in the embodiments can be combined with each other, wherein the same components are indicated by the same reference numerals.

[0015] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification, claims and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product or device.

[0016] First Implementation Method

[0017] like Figure 1 In the factual manner shown, the method of the present invention includes: S1-S3.

[0018] S1, based on the bidirectional porosity theory, obtains the single reflectance of the double-layer canopy.

[0019] S2, based on the theory of spectral invariance, obtains the multiple reflectance of the double canopy.

[0020] S3, the total reflectance of the double canopy is obtained based on the single reflectance and multiple reflectance of the double canopy.

[0021] Second Implementation Method

[0022] like Figure 2 and Figure 3 In the embodiments shown, the method of the present invention includes S1-S5.

[0023] S1. Input the spectral vector coefficients of the upper and lower canopy leaves into the General Spectral Vector-Leaf (GSV-L) model to calculate the reflectance and transmittance spectral data of the upper and lower canopy leaves across the entire 400-2400 nm wavelength range. The specific calculation process is as follows:

[0024]

[0025] Where, ρ L (λ) and τ L (λ) represents the leaf reflectance and transmittance simulated by the GSV-L model, respectively, u LRi (λ) and u LTi (λ) are the spectral vectors of leaf reflectance and transmittance, respectively, and c Li The coefficients are the leaf spectral vectors.

[0026] S2. Input the soil reflectance spectral vector coefficients into the General Spectral Vector (GSV) soil reflectance model to calculate the soil reflectance spectral data across the entire 400-2400 nm wavelength range. The specific calculation process is as follows:

[0027]

[0028] Where, ρ G (λ) represents the soil reflectance simulated by the GSV model, u Si (λ) is the soil reflectance spectral vector, c Si represents the coefficient of the soil reflectance spectral vector.

[0029] S3. Input the structural parameters of the upper and lower canopies, the reflectance and transmittance spectra of the upper and lower canopy leaves obtained in step S1, the solar-observation geometry, and the soil reflectance spectrum obtained in step S2 into the CANOP model, and calculate the single reflectance of the double-layer vegetation canopy using the surface scattering phase function, bidirectional porosity, and hotspot factor.

[0030] The specific calculation process is as follows: R Single (λ,Ω) represents the single reflectance of the vegetation-soil system. and R represents the single reflectance of the upper and lower vegetation canopy layers, respectively. S (λ,Ω) represents the single reflectance of the soil, and the following exists:

[0031]

[0032] in, Let u be the solar radiation-visible leaf area of ​​the j-th vegetation canopy layer. L (j) Let be the leaf area density of the j-th vegetation canopy. For sun-exposed - visible soil, ρ G (λ) represents the soil reflectance simulated by the GSV model, and Ω represents the solar-observation geometry. Let be the scattering coefficient of direct sunlight in the j-th layer of the vegetation canopy towards the observation direction. Then:

[0033]

[0034] Where, ρ L (h) (λ) and τ L (j) (λ) represents the leaf reflectance and transmittance of the j-th vegetation canopy layer simulated by the GSV-L model. (j) (θ l ) represents the average backscattering coefficient of the j-th vegetation canopy layer, sof (j) (θ l ) represents the average forward surface scattering coefficient of the j-th vegetation canopy layer. Let be the zenith angle of the leaves in the j-th layer of the vegetation canopy.

[0035] S4. Input the structural parameters of the upper and lower vegetation canopies, the leaf reflectance and transmittance spectra obtained in step S1, the solar-observation geometry, and the soil reflectance spectra obtained in S2 into the CANOP model, and use the spectral invariance theory to calculate the multiple reflectance between the double-layer vegetation canopy and the soil background.

[0036] In one implementation, step S4 includes steps S41-S43.

[0037] S41 uses the spectral invariance theory to calculate the reflectance and transmittance of the upper and lower vegetation canopies in black soil and soil problems.

[0038] The specific calculation process is as follows: and Let be the downward reflectance and upward transmittance of the j-th layer of vegetation canopy in the soil problem, respectively. and These represent the upward multiple reflectance and downward transmittance of the j-th vegetation canopy layer in the black soil problem.

[0039]

[0040] in, It is the leaf single-scatter albedo (sum of reflectance and transmittance) simulated by GSV-L in the j-th layer of vegetation canopy. It is the directional transmittance of the j-th vegetation canopy layer under diffuse radiation conditions. It is the directional transmittance of the j-th layer of vegetation canopy in the direction of the sun. It is the interception of the j-th layer of vegetation canopy in the direction of the sun. The escape probability ρ of the multiple (>1) directions reflected upward by the j-th layer of vegetation canopy. (j) (Ω) is equal to the multiple-order (>1) directional escape probability τ of downward transmission. (j) (Ω), exists:

[0041]

[0042] Among them, i (j) (Ω) represents the directional interception of the j-th vegetation canopy layer, LAI (j) Let be the leaf area index of the j-th vegetation canopy. Similarly, let be the multi-order (>1) hemispherical escape probability reflected upwards by the j-th vegetation canopy. Equal to the multi-order (>1) hemispherical escape probability of downward transmission exist:

[0043]

[0044] Among them, the hemispherical interception of the j-th layer of vegetation canopy under diffuse radiation conditions for:

[0045]

[0046] The multi-order (>1) re-collision probability p of the j-th layer of vegetation canopy (j) for:

[0047]

[0048] S42, the total reflectance and total transmittance of the double-layer vegetation canopy are calculated using the superposition-doubling method.

[0049] The specific calculation process is as follows: In soil problems, the total reflectance r of a double-layered vegetation canopy pointing downwards... S and the total transmittance T upward S for:

[0050]

[0051] Total multiple reflectance of double-layered vegetation canopy upwards in black soil problems and total downward transmittance T BS for:

[0052]

[0053] S43, the solutions to the black soil and soil problems are superimposed to calculate the total reflectance of the vegetation-soil system. The specific calculation process is as follows: R m (λ,Ω) represents the multiple reflectance within the vegetation. For the multi-reflectivity of vegetation and soil interior in soil problems:

[0054]

[0055] S5. The single and multiple reflectances of the above vegetation-soil system are combined to obtain the double-layer vegetation canopy reflectance in the full 400-2400nm band with different leaf spectral characteristics and canopy structure features.

[0056] The specific calculation process is as follows: R(λ,Ω) is the total reflectance of the double-layered vegetation canopy, and the following exists:

[0057] R(λ,Ω)=R single (λ,Ω)+R Multiple (λ,Ω) (23)

[0058] This invention has been compared and verified with the one-dimensional double-layer vegetation canopy radiative transfer model ACRM, the three-dimensional computer simulation model DART, and measured data of double-layer rice canopy in spectral and angular spaces. The results show that the CANOP model can accurately simulate the multi-angle and hyperspectral reflectance of the double-layer vegetation canopy.

[0059] This invention provides a two-layer vegetation canopy radiative transfer model, with the following specific innovations:

[0060] (1) Compared with the existing double-layer vegetation canopy radiative transfer model based on the four-flux theory, which assumes that multiple scattering is isotropic and has a complex principle, the CANOP model uses the spectral invariance theory to calculate the multiple reflections of the directional double-layer vegetation canopy. It does not require the calculation of complex layer scattering matrices, and has a simple principle and high accuracy.

[0061] (2) The CANOP model couples the general spectral vector leaf model GSV-L and the general spectral vector soil reflectance model GSV. It requires fewer leaf and soil input parameters and can focus on inverting canopy structure parameters from remote sensing data.

[0062] The embodiments described above are merely preferred embodiments of the present invention. The terms "in one embodiment," "in another embodiment," "in yet another embodiment," or "in still another embodiment" used in this specification all refer to one or more of the same or different embodiments according to this disclosure. Ordinary variations and substitutions made by those skilled in the art within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the full-band reflectivity radiative transfer of a double-layered vegetation canopy, characterized in that, include: S1, based on the bidirectional porosity theory, obtains the single reflectance of the double-layer canopy; S2, based on the theory of spectral invariance, obtains the multiple reflectance of the double-layer canopy; S3, the total reflectance of the double canopy is obtained based on the single reflectance and multiple reflectance of the double canopy.

2. The method according to claim 1, characterized in that, In step S1, the single reflectance of the double-layer vegetation canopy is calculated based on the reflectance and transmittance spectra of the upper and lower canopy leaves and the soil reflectance spectrum, using the bidirectional porosity theory. In step S2, based on the reflectance and transmittance spectra of the upper and lower canopy leaves, the multiple reflectance of the double-layer vegetation canopy and its relationship with the soil background is calculated using the spectral invariance theory. In step S3, the single reflection and multiple reflection rates are combined to obtain the double-layer vegetation canopy reflectance.

3. A method for calculating the full-band reflectivity radiative transfer of a double-layered vegetation canopy, characterized in that, include: S1, based on the leaf spectral vectors of the upper and lower canopies, calculates the reflectance and transmittance spectra of the upper and lower canopy leaves; S2, based on the soil reflectance spectral vector, the soil reflectance spectrum is calculated; S3, based on the reflectance and transmittance spectra of the upper and lower canopy leaves, as well as the soil reflectance spectrum, the single reflectance of the double-layer vegetation canopy was calculated based on the bidirectional porosity theory. S4. Based on the reflectance and transmittance spectra of the upper and lower canopy leaves, the multiple reflectance of the double-layer vegetation canopy and its relationship with the soil background is calculated using the spectral invariance theory. S5, combine the single reflection and multiple reflection rates to obtain the double-layer vegetation canopy reflectance.

4. The method according to claim 3, characterized in that, In step S1, the reflectance and transmittance spectra of the upper and lower canopy leaves are obtained using the general spectral vector leaf model GSV-L; In step S2, the soil reflectance spectrum is obtained using the General Spectral Vector Soil Reflectance Model (GSV).

5. The method according to claim 4, characterized in that, In step S3, the single reflectance of the double-layer vegetation canopy is calculated using the surface scattering phase function, bidirectional porosity, and hotspot factor.

6. The method according to claim 4, characterized in that, In step S4, the multiple reflectance of the double-layered vegetation canopy and its relationship with the soil background is calculated using the spectral invariance theory.

7. The method according to claim 5, characterized in that, In step S3, the single reflectance of the double-layer vegetation canopy is calculated based on the structural parameters of the upper and lower canopies, the reflectance and transmittance spectra of the upper and lower canopy leaves obtained in step S1, the solar-observation geometry, and the soil reflectance spectrum obtained in step S2.

8. The method according to claim 6, characterized in that, In step S4, based on the structural parameters of the upper and lower vegetation canopies, the leaf reflectance and transmittance spectra obtained in step S1, the solar-observation geometry, and the soil reflectance spectra obtained in step S2, the multiple reflectance between the double-layer vegetation canopy and the soil background is calculated.

9. The method according to claim 8, characterized in that, Step S4 includes: S41, using the spectral invariance theory to calculate the reflectance and transmittance of the upper and lower vegetation canopies in black soil and soil problems; S42, the total reflectance and total transmittance of the double-layer vegetation canopy were calculated using the superposition-doubling method; S43 calculates the total reflectance of the vegetation-soil system by superimposing the solutions to the black soil and soil problems.

10. A system for calculating the full-band reflectivity radiative transfer of a double-layered vegetation canopy, comprising: A computer-executable program that, when executed, performs the method described in any one of claims 1-9 above.

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